In the field of wireless communication, especially in mobile communication, a variety of information such as image and data in addition to voice is becoming transmission targets in recent years. It is anticipated that the demand for high-speed transmission becomes further increased in the future, and to perform high-speed transmission, a wireless transmission scheme, which utilizes limited frequency resources more effectively to achieve high transmission efficiency, has been required.
OFDM (Orthogonal Frequency Division Multiplexing) is one of wireless transmission techniques, for meeting these requirements. OFDM is one of multicarrier communication techniques, whereby data is transmitted in parallel using a large number of subcarriers, and it is known that OFDM provides high frequency efficiency and reducing inter-symbol interference under a multipath environment and is effective to improve transmission efficiency.
In OFDM, the quality of each subcarrier may greatly fluctuate depending on frequency selective fading due to multi-path. In this case, since the signal allocated to a subcarrier at a position of a fading valley has a poor quality, thus making demodulation thereof difficult, the quality of the signal needs to be improved so as to make demodulation possible.
A technique for improving the quality in OFDM is the so-called repetition. The repetition is a technique in which a certain symbol is repeated to generate a plurality of same symbols, and these same symbols are allocated to a plurality of different subcarriers or different times to be transmitted. These same symbols are subjected to maximum ratio combining at the receiver side, whereby a diversity gain can be obtained (refer to Non-Patent Document 1, for instance).
Non-Patent Document 1: Maeda, Atarashi, Kishiyama, Sawahashi “Performance Comparison between OFCDM and OFDM in a Forward Link Broadband Channel”, Technical Report of IEICE.RCS2002-162, August 2002